Schottky diodes are commonly used in applications requiring fast switching, for example, in power circuits. Also, while standard silicon diodes have a forward voltage drop of about 0.6 volts, Schottky diode's voltage drop at forward biases of around 1 mA may be in the range of 0.15 V to 0.45 V, making it useful in voltage-clamping applications and in applications for preventing transistor saturation. Schottky diode's higher current densities further distinguish it from other diodes.
FIG. 1 illustrates a cross-sectional view of a conventional Schottky diode 100, which is formed on p-type substrate 102. High-voltage p-well 104 is formed as a ring encircling high-voltage n-well 106. Shallow trench isolation ring 108 also encircles high-voltage n-well 106 and the inner portion of high-voltage p-well 104. Metal-containing layer 110 is formed over high-voltage p-well 104 and high-voltage n-well 106 to form a Schottky diode. N-type buried layer 112 separates Schottky diode 100 from the underlying p-type substrate 102, and provides electrical connection to the pickup regions 114 through high-voltage n-well 116.
Schottky diode 100 suffers from a low breakdown voltage. FIG. 2 illustrates an I-V curve of Schottky diode 100, wherein the X-axis indicates the reverse voltage VR applied on Schottky diode 100, and the Y-axis indicates the leakage current IR. It is noted that with the increase in the reverse voltage VR, the leakage current IR continues to increase significantly. Further, the Ion/Ioff ratio, which represents the Schottky diode's ability to provide forward currents without causing significant leakage currents (when reverse biased), is only about 1.2×103, which is unsatisfactory for applications demanding Schottky diodes with high performances. Schottky diodes with reduced leakage currents and increased on-currents are thus needed.